When observing a surface illuminated by coherent light or by the projection of coherent light onto the surface, an illumination pattern which appears irregularly bright in the form of a “speckle pattern” may be perceived in the far field of the reflected light. The speckle pattern may arise during imaging of the illuminated surface for example onto the retina of the eye or onto a spatially resolving detector system through interference effects of the light reflected at surface structures of the surface. Typical surface structures are usually the result of surface roughness. In the event of continuous modification of the illuminated area of the surface or of the eye or detector position, the continuously changing speckle pattern may be perceived in a mostly undesired manner as flickering.